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Temperature conversion formulas: Fahrenheit to Celsius: C = (F - 32) x 5/9, or simplified (F - 32) / 1.8. Celsius to Fahrenheit: F = (C x 9/5) + 32, or C x 1.8 + 32. Kelvin to Celsius: C = K - 273.15. Kelvin to Fahrenheit: F = (K - 273.15) x 9/5 + 32. Quick mental conversion tricks: 0 C = 32 F (water freezes), 100 C = 212 F (water boils at 1 atm), 37 C = 98.6 F (normal body temperature), 20 C = 68 F (room temperature), -40 C = -40 F (the only point where both scales agree). For rough estimation Celsius to Fahrenheit: double the Celsius value and add 30 (20 C → 70 F, actual 68 F). Temperature reference points: comfortable indoor 20 to 22 C (68 to 72 F), refrigerator 3 to 5 C (37 to 40 F), freezer -18 C (0 F), oven moderate 180 C (350 F), oven hot 230 C (450 F). The Kelvin scale is used in science and engineering because 0 K represents absolute zero (lowest possible temperature). Global scientific standard is Celsius for most applications; Fahrenheit is primarily used in the United States, Bahamas, Cayman Islands, Liberia, Palau, and the Federated States of Micronesia.

Weight and mass conversions. Pounds to kilograms: kg = lbs x 0.453592 (or divide by 2.2046). Kilograms to pounds: lbs = kg x 2.2046. Ounces to grams: g = oz x 28.3495. Grams to ounces: oz = g x 0.035274. Pounds to grams: g = lbs x 453.592. Quick reference: 1 lb = 453.6 g = 16 oz; 1 kg = 2.2 lbs = 1000 g; 1 oz = 28.35 g. Common conversions: 150 lbs = 68 kg, 100 kg = 220 lbs, 1 oz = 28.35 g, 8 oz (half pound) = 227 g. For cooking, many recipes use weight for accuracy: 1 cup all-purpose flour weighs 125 g (4.4 oz), 1 cup granulated sugar 200 g (7 oz), 1 cup butter 227 g (8 oz). Different scale systems: US avoirdupois is standard for most applications; troy ounces (31.103 g, 12 troy ounces per troy pound) are used for precious metals — a 1-oz gold coin is actually 1 troy oz (31.1 g); pharmaceutical weights historically used apothecaries' system but now use metric exclusively. Body weight measurements: stones (UK/Ireland): 1 stone = 14 lbs = 6.35 kg. For international shipping, declared weight in kilograms is standard for most carriers globally except US domestic (pounds).

Distance conversions between imperial and metric. Miles to kilometers: km = miles x 1.60934. Kilometers to miles: miles = km x 0.62137 (or divide by 1.60934). Quick reference: 1 mile = 1.609 km = 1609 meters = 5280 feet; 1 km = 0.621 miles; marathon distance 26.2 miles = 42.195 km. Mental math shortcut: multiply miles by 8 and divide by 5 for kilometers (close approximation), or add 60 percent. Examples: 60 mph = 97 kph; 100 kph = 62 mph; 5K run = 3.1 miles; 10K run = 6.2 miles. Nautical miles (used in aviation and shipping): 1 nautical mile = 1.852 km = 1.151 statute miles. Speed: 1 knot (nautical mph) = 1.852 kph = 1.151 mph. Commercial airliner cruising: 500 to 550 mph = 805 to 885 kph = 435 to 475 knots. Other distance units: foot 0.3048 m, yard 0.9144 m (1 m = 1.0936 yd), inch 2.54 cm. Astronomical units: 1 light-year = 9.46 trillion km (5.88 trillion miles); 1 astronomical unit (Earth-Sun distance) = 149.6 million km. When driving internationally, note speed limits: US/UK use mph, Canada/Europe/most world use kph. GPS apps auto-convert based on locale settings.

Volume conversions. US gallons to liters: L = US gal x 3.78541. Liters to US gallons: US gal = L x 0.26417. Imperial (UK) gallons: 1 UK gal = 4.54609 L (larger than US gallon). US to Imperial: 1 US gal = 0.833 UK gal; 1 UK gal = 1.201 US gal. Quick reference: 1 US gal = 3.79 L = 128 fl oz; 1 L = 0.264 US gal = 33.8 fl oz; 1 UK gal = 4.55 L = 160 UK fl oz. Fluid ounce differences: 1 US fl oz = 29.574 ml; 1 UK fl oz = 28.413 ml (smaller). Common conversions: 1 gal milk (US) = 3.79 L; car tank 15 US gal = 56.8 L; barrel (petroleum) = 42 US gal = 158.99 L (or 35 UK gal). Fuel efficiency: mpg (US) to L/100km: divide 235.215 by mpg. Example: 30 mpg US = 7.84 L/100km; 25 mpg US = 9.4 L/100km. Cooking volume: 1 cup US = 236.588 ml; 1 cup UK = 284 ml; 1 tablespoon US = 14.787 ml; 1 teaspoon US = 4.929 ml. Different countries use different measuring cup standards: US (240 ml), UK/metric (250 ml), Australia (250 ml), Japan (200 ml). For recipes, use weight measurements when possible for consistency across regions.

Digital storage uses two different conventions: binary (1024-based, used by operating systems) and decimal (1000-based, used by storage manufacturers). IEC binary prefixes (1024-based): 1 kibibyte (KiB) = 1024 bytes; 1 mebibyte (MiB) = 1024 KiB = 1,048,576 bytes; 1 gibibyte (GiB) = 1024 MiB; 1 tebibyte (TiB) = 1024 GiB. SI decimal prefixes (1000-based): 1 kilobyte (KB) = 1000 bytes; 1 megabyte (MB) = 1000 KB = 1,000,000 bytes; 1 gigabyte (GB) = 1000 MB; 1 terabyte (TB) = 1000 GB. This creates the familiar discrepancy: a 1 TB hard drive shows about 931 GB in Windows (which uses binary math but displays with decimal labels). Practical sizes: single text email 10 to 50 KB; high-resolution photo 2 to 10 MB; 4K video per minute 300 to 700 MB; HD movie 2-hour 3 to 5 GB; 4K movie 25 to 50 GB; typical SSD 500 GB to 2 TB; Blu-ray disc 25 to 100 GB. Network speed uses bits (lowercase b): 1 byte = 8 bits. Internet connection of 100 Mbps = 12.5 MB per second (divide Mbps by 8). Downloading a 5 GB file at 100 Mbps: 5000 MB / 12.5 MB/s = 400 seconds (6.7 minutes). Enterprise storage: 1 petabyte (PB) = 1000 TB = 1 million GB; 1 exabyte (EB) = 1000 PB. Global data volume crossed 180 zettabytes in 2025 (IDC estimate).